<!DOCTYPE html>
<html lang="en" style="font-size: 25px">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <meta name="viewport"
        content="width=device-width,initial-scale=1.0,minimum-scale=1,maximum-scale=1,user-scalable=no"/>
  <title>Title</title>
  <style>
    body {
      background: rebeccapurple;
    }

    #c1 {
      background: white;
      /* canvas透明 */
      background: rgba(255, 255, 255, 0);
    }
  </style>
</head>
<body>
<canvas id="c1" width="15rem" height="15rem">
  <span>不支持canvas</span>
</canvas>
<script src="demo1.js"></script>
</body>
</html>
